Interzeolite transformation of FER into thin-platelet SSZ-39 for highly hydrothermally stable Cu-based NH3-SCR catalysts

• Rapid interzeolite transformation of FER to thin-platelet SSZ-39 (AEI) in 8 h. • FER-derived S5R units enable rapid hydrolysis-reconstruction crystallization of AEI. • High NO x conversion is retained after severe hydrothermal aging at 900 °C for 6 h. • Paired framework Al stabilizes Cu 2+ −2Z species and suppresses CuO x aggregation. Durable ammonia selective catalytic reduction (NH 3 -SCR) catalysts that retain activity under extreme hydrothermal conditions are essential to reduce lifecycle emissions and catalyst replacement frequency in diesel aftertreatment. We report a process-intensified interzeolite transformation route that utilizes low-silica, platelet-like FER zeolite as the aluminum source. This route synthesizes high-silica, thin-platelet SSZ-39 (AEI) at 170 °C, achieving high crystallinity within 8 h under optimized conditions. Time-resolved XRD, TG–DSC, FT-IR, and SEM suggest that AEI formation proceeds through alkaline hydrolysis and reconstruction of labile single five-membered ring (S5R) units inherited from FER. Cu/AEI catalysts derived from FER and FAU precursors with comparable Si/Al ratios and Cu loadings were evaluated for NH 3 -SCR and durability. After severe hydrothermal aging at 900 °C for 6 h, the FER-derived catalyst maintains substantially higher NO x conversion than its FAU-derived counterpart and exhibits mitigated N 2 O formation at high temperature. Spectroscopic analyses link this resilience to a higher retained fraction of paired framework Al in the FER-derived zeolite, which stabilizes Cu 2+ -2Z species and suppresses aggregation into CuO x clusters during aging. These findings demonstrate that precursor-enabled Al distribution control via interzeolite transformation offers an engineering-relevant strategy to improve the durability and environmental performance of Cu/AEI SCR catalysts.